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16 Oct 2000

Volume 77, Issue 16, pp. 2437-2616

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Probing capped and uncapped mesoporous low-dielectric constant films using positron annihilation lifetime spectroscopy

Mihail P. Petkov, Marc H. Weber, Kelvin G. Lynn, and Kenneth P. Rodbell

Appl. Phys. Lett. 77, 2470 (2000); http://dx.doi.org/10.1063/1.1318238 (3 pages) | Cited 21 times

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We have measured uncapped mesoporous low-dielectric-constant films using positron annihilation lifetime spectroscopy (PALS), a nondestructive technique, which yields both pore-size distributions and the threshold for pore interconnectivity. Pairs of fully cured capped and uncapped identical films, initially containing 5%–50% porogen additions, exhibited similar signatures in PALS, establishing a technique in which film capping is unnecessary. We also found that it was possible to distinguish between closed and percolated pores, without film capping, by comparing lifetime spectra of a film taken using different detector configurations. Interconnected pores were observed in cured samples, which had greater than 20% porogen additions. © 2000 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
78.70.Bj Positron annihilation
85.40.Ls Metallization, contacts, interconnects; device isolation
77.55.-g Dielectric thin films
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials

Efficient photovoltaic energy conversion in pentacene-based heterojunctions

J. H. Schön, Ch. Kloc, and B. Batlogg

Appl. Phys. Lett. 77, 2473 (2000); http://dx.doi.org/10.1063/1.1318234 (3 pages) | Cited 25 times

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We have prepared heterojunction devices based on ZnO and both pentacene single crystals and thin films. Their photovoltaic properties have been studied. Bromine doping is found to improve significantly the performance of such devices and solar-energy conversion efficiencies up to 4.5% are achieved for single-crystal devices. In addition, efficiencies exceeding 2% are realized in thin-film devices on flexible plastic substrates. These results demonstrate that efficient photovoltaic energy conversion is possible with organic semiconductors. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.61.Ph Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects

Effect of Sb doping on the thermoelectric properties of Ti-based half-Heusler compounds, TiNiSn1−xSbx

S. Bhattacharya, A. L. Pope, R. T. Littleton, Terry M. Tritt, V. Ponnambalam, Y. Xia, and S. J. Poon

Appl. Phys. Lett. 77, 2476 (2000); http://dx.doi.org/10.1063/1.1318237 (3 pages) | Cited 53 times

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Half-Heusler alloys (MgAgAs type) with the general formula MNiSn where M is a group IV transition metal (Hf, Zr, or Ti) are currently under investigation for potential thermoelectric materials. These materials exhibit a high negative thermopower (−40 to −250 μV/K) and low electrical resistivity values (0.1–8 mΩ cm) both of which are necessary for a potential thermoelectric material. Results are presented in this letter regarding the effect of Sb doping on the Sn site (TiNiSn1−xSbx). The Sb doping leads to a relatively large power factor of (0.2–1.0) W/m K at room temperature for small concentrations of Sb. These values are comparable to that of Bi2Te3 alloys, which are the current state-of-the-art thermoelectric materials. The power factor is much larger at T ≈ 650 K where it is over 4 W/m K making these materials very attractive for potential power generation considerations. © 2000 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Ga Transition-metal compounds
72.20.Fr Low-field transport and mobility; piezoresistance

Faceted inversion domain boundary in GaN films doped with Mg

L. T. Romano, J. E. Northrup, A. J. Ptak, and T. H. Myers

Appl. Phys. Lett. 77, 2479 (2000); http://dx.doi.org/10.1063/1.1318731 (3 pages) | Cited 51 times

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Homoepitaxial GaN films, doped with Mg, were grown by rf-plasma molecular-beam epitaxy on Ga-polarity (0001) templates. Convergent-beam electron diffraction analysis establishes that the film polarity changes from [0001] to [000math] when the Mg flux during growth is approximately 1 ML/s. Secondary ion mass spectrometry indicates a doping concentration of ∼ 1020 cm−3 in the film where the inversion occurs, and a reduced Mg incorporation in the [000math] material. Transmission electron microscopy shows that the inversion domain boundary is faceted predominantly along the {0001} and {h,h,−2h,l} planes, with l/h approximately equal to 3. Using first-principles total energy calculations, we show that the {h,h,−2h,l} segments of the boundary are stabilized by the incorporation of Mg in threefold coordinated lattice sites. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.uj III-V and II-VI semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors

Comparison of nitrogen incorporation in molecular-beam epitaxy of GaAsN, GaInAsN, and GaAsSbN

J. C. Harmand, G. Ungaro, L. Largeau, and G. Le Roux

Appl. Phys. Lett. 77, 2482 (2000); http://dx.doi.org/10.1063/1.1318228 (3 pages) | Cited 49 times

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The incorporation of nitrogen in the low percentage range is investigated in a different III–V compound matrix. The materials are grown by molecular-beam epitaxy with a nitrogen radio-frequency plasma source. For equivalent growth conditions, the same rate of N incorporation is found for GaAsN and GaInAsN. However, this N incorporation rate is significantly enhanced in the GaAsSbN alloy. These observations support a discussion on the reactive nitrogen species. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology

Molecular beam epitaxial growth of atomically smooth scandium nitride films

Hamad Al-Brithen and Arthur R. Smith

Appl. Phys. Lett. 77, 2485 (2000); http://dx.doi.org/10.1063/1.1318227 (3 pages) | Cited 31 times

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High quality scandium nitride films have been grown on magnesium oxide (001) substrates by molecular beam epitaxy using a rf plasma source for nitrogen. Both reflection high energy electron diffraction and x-ray diffraction confirm that these films have (001)-orientation. Atomic force microscopy reveals a surface morphology consisting of large plateaus and pyramids. The plateaus are found to be atomically smooth and have a 1×1 surface structure, as revealed by in situ scanning tunneling microscopy. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Domain mapping of periodically poled lithium niobate via terahertz wave form analysis

Y.-S. Lee, T. Meade, M. L. Naudeau, T. B. Norris, and A. Galvanauskas

Appl. Phys. Lett. 77, 2488 (2000); http://dx.doi.org/10.1063/1.1318725 (3 pages) | Cited 12 times

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We demonstrate a nondestructive probing technique to investigate the inner crystal domain structure of ferroelectric crystals by analyzing the terahertz wave forms generated by optical rectification. Quantitative analysis of the domain structure has been performed for the domain width in periodically poled lithium niobate. Simulation results show that the terahertz wave form analysis reproduces root-mean-square domain width fluctuations. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
42.70.Mp Nonlinear optical crystals
77.22.Ej Polarization and depolarization

Molecular beam epitaxy growth of GaN on C-terminated 6H–SiC (000math) surface

Z. P. Guan, A. L. Cai, J. S. Cabalu, H. L. Porter, and S. Huang

Appl. Phys. Lett. 77, 2491 (2000); http://dx.doi.org/10.1063/1.1318723 (3 pages) | Cited 9 times

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We report the results of successful growth of GaN on the C-terminated surface of SiC. A combination of direct heating and hydrogen plasma treatment was employed for surface preparation. High-quality epitaxy was achieved in epilayers as thin as 2000 Å, as evidenced by the x-ray diffraction full width at half maximum of 90 arc sec and 4.2 K donor-bound exciton peak width of 1.4 meV. The epilayers exhibit clear signatures of compressive strain, suggesting a more favorable growth mode than can be achieved on the Si-terminated surface. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Photorefraction in LiNbO3 as a function of [Li]/[Nb] and MgO concentrations

Y. Furukawa, K. Kitamura, S. Takekawa, A. Miyamoto, M. Terao, and N. Suda

Appl. Phys. Lett. 77, 2494 (2000); http://dx.doi.org/10.1063/1.1318721 (3 pages) | Cited 69 times

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Photorefractive damage, photoconductivities, and photogalvanic currents of LiNbO3 single crystals have been investigated as a function of [Li]/[Nb] and MgO concentrations. Near stoichiometric LiNbO3 single crystal, having large [Li]/[Nb] ratios of 0.993, shows lower photorefractive damage resistance than congruent LiNbO3. However, crystals doped with a small amount of MgO (>0.78 mol %) exhibit no measurable photorefractive damage at 532 nm to intensities of as much as 2 MW/cm2. This remarkable decrease of photorefraction that was found can be attributed to the decrease of saturated space charge field results from a combination of the increased photoconductivity and the decreased photogalvanic current of the crystal. © 2000 American Institute of Physics.
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42.70.Gi Light-sensitive materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.40.+w Photoconduction and photovoltaic effects
77.22.Jp Dielectric breakdown and space-charge effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
61.66.Bi Elemental solids
61.66.Dk Alloys

Influence of growth direction on order–disorder transition in (GaAs)1−x(Ge)2x semiconductor alloys

A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal

Appl. Phys. Lett. 77, 2497 (2000); http://dx.doi.org/10.1063/1.1318722 (3 pages) | Cited 6 times

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We provide direct evidence of the dependence of the critical concentration of IV-type atoms at the order–disorder transition in ternary metastable (III–V)–IV, zincblende–diamond semiconductor alloys on the growth direction. The excellent agreement between the experimental and model predicted critical concentrations is evidence that the atomic ordering in these alloys is ruled almost entirely by substrate geometry. In this letter, we report the observation of the critical concentration dependence on substrate orientation in (GaAs)1−x(Ge2)x metastable alloys, epitaxially grown on (001), (111), (112), and (113) oriented GaAs. A different long-range order parameter behavior with Ge concentration is obtained for each growth direction. The Ge critical concentrations observed are 0.36, 0.96, 0.59, and 0.50±0.03, for the orientations listed above, values that compare well with those obtained from a Monte Carlo simulation of the growth, 0.33, 1.0, 0.64, and 0.54, respectively. © 2000 American Institute of Physics.
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64.70.K- Solid-solid transitions
68.55.Nq Composition and phase identification
64.60.Cn Order-disorder transformations
64.60.My Metastable phases
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
02.70.Rr General statistical methods

Optical microcavities using highly luminescent films of semiconductor nanocrystals

Chris E. Finlayson, David S. Ginger, and Neil C. Greenham

Appl. Phys. Lett. 77, 2500 (2000); http://dx.doi.org/10.1063/1.1318720 (3 pages) | Cited 23 times

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Colloidally grown CdSe nanocrystals with epitaxial ZnS shells show highly efficient, size-tunable luminescence. We report the incorporation of films of these core-shell nanocrystals into wavelength-scale, high-Q, planar microcavities. Under optical excitation, we find that emission from the nanocrystals couples to the discrete optical modes of the microcavity. The broad free-space emission spectrum of the nanocrystals is modified by the presence of the microcavity, giving a series of sharp emission lines with wavelengths determined by the cavity dimension. Our experiments demonstrate that microcavities with semiconductor emitters can be conveniently fabricated using spin-coating techniques. We find that, at room temperature, the microcavity emission spectrum is independent of excitation intensity for excitation densities up to approximately one electron–hole pair per nanocrystal. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
42.79.Wc Optical coatings
81.05.Dz II-VI semiconductors

Observation of long photoluminescence decay times for high-quality GaN grown by metalorganic chemical vapor deposition

Ho Ki Kwon, C. J. Eiting, D. J. H. Lambert, M. M. Wong, R. D. Dupuis, Z. Liliental-Weber, and M. Benamara

Appl. Phys. Lett. 77, 2503 (2000); http://dx.doi.org/10.1063/1.1318396 (3 pages) | Cited 12 times

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GaN epitaxial layers with different crystalline quality grown on sapphire substrates by metalorganic chemical vapor deposition are investigated using time-resolved photoluminescence at 300 K. It is found that the time-dependent photoluminescence of low-quality GaN decays faster than that of the high-quality GaN films. The time constants for the dual-exponential decay of the photoluminescence are calculated to be 50 and 250 ps for high-quality undoped GaN and 30 ps for low-quality undoped GaN. For high-quality Si-doped GaN, time constants of 150 and 740 ps are extracted while corresponding time constants of 40 and 200 ps are measured for low-quality Si-doped GaN. We believe that the time constant of 740 ps measured for our high-quality Si-doped GaN is the longest ever reported for thin GaN/sapphire films. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Strong blue emission from As doped GaN grown by molecular beam epitaxy

A. J. Winser, S. V. Novikov, C. S. Davis, T. S. Cheng, C. T. Foxon, and I. Harrison

Appl. Phys. Lett. 77, 2506 (2000); http://dx.doi.org/10.1063/1.1318394 (3 pages) | Cited 22 times

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Arsenic doped GaN grown by molecular beam epitaxy has been studied by room temperature photoluminescence. In addition to the wurzite band edge transition, luminescence from the cubic phase and very strong blue emission at ∼2.6 eV are observed. The intensities of the blue and the cubic band edge emissions have a power law dependence on the As2 flux. The formation of the cubic phase has been explained by the initial formation of GaAs before substitution of the As by the more reactive N. The intensity of the blue emission at room temperature of the As doped samples is more than an order of magnitude stronger than the band edge emission in undoped samples. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Effect of overgrowth temperature on the photoluminescence of Ge/Si islands

O. G. Schmidt, U. Denker, K. Eberl, O. Kienzle, and F. Ernst

Appl. Phys. Lett. 77, 2509 (2000); http://dx.doi.org/10.1063/1.1318729 (3 pages) | Cited 47 times

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Ge/Si islands grown with molecular-beam epitaxy at 630 °C are overgrown with Si at different temperatures Tcap, and their photoluminescene spectra are recorded. Both the island-related and wetting-layer-related energy transitions redshift with lowered Tcap, which is explained by reduced material intermixing. The mandatory growth interruption, which is introduced during the temperature drop, causes island ripening and shifts the island (wetting layer) photoluminescence peaks slightly to lower (higher) energies. The growth interruption quenches the quantum efficiency of the wetting layer by more than an order of magnitude, whereas the island-related photoluminescence intensity even slightly increases. The island’s superior resistance against growth interruptions, and hence interface contamination, is explained by effective carrier localization in the Ge nanostructures. Room-temperature photoluminescence is reported for Ge islands overgrown at 460 °C. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors

Structural analysis of InxGa1−xN single quantum wells by coaxial-impact collision ion scattering spectroscopy

M. Sumiya, S. Nakamura, S. F. Chichibu, K. Mizuno, M. Furusawa, and M. Yoshimoto

Appl. Phys. Lett. 77, 2512 (2000); http://dx.doi.org/10.1063/1.1318933 (3 pages) | Cited 2 times

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The structures of InxGa1−xN single quantum wells (SQWs) on 3-μm-thick GaN layer for the ultraviolet, blue, and green light-emitting devices were investigated by coaxial-impact collision ion scattering spectroscopy (CAICISS). The possibility that CAICISS could analyze structural fluctuation of the ternary system like InxGa1−xN was demonstrated. It was found that In incorporated into InGaN SQWs occupied the substitutional site of Ga atom having Ga-face (+c) polarity. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.66.Fd III-V semiconductors

Refractive index dispersion functions of solid-phase polymers by multicolor optical diffraction

J. V. Ford, B. G. Sumpter, D. W. Noid, M. D. Barnes, and J. U. Otaigbe

Appl. Phys. Lett. 77, 2515 (2000); http://dx.doi.org/10.1063/1.1318940 (3 pages) | Cited 4 times

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We show that fourth-order dispersion functions of solid-phase polymers can be determined by multicolor optical diffraction. Electrodynamically trapped microparticles of polyethylene glycol with different molecular weights were probed by two-dimensional optical diffraction with four different laser wavelengths (632.8, 514.5, 488.0, and 457.9 nm); subsequent Mie analysis of one-dimensional scattering patterns yielded size and refractive index (both real and imaginary parts). Using a single wavelength as a size reference, the nonlinear dependence of the refractive index of solid (nonevaporating) polymer microparticles was determined by finding the refractive index for a given wavelength that best matched a Mie calculation subject to the reference size constraint. The experimentally determined refractive index values were fit to a standard fourth-order Cauchy function to obtain values for n0, n1, and n2. © 2000 American Institute of Physics.
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42.70.Jk Polymers and organics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.25.Fx Diffraction and scattering
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Enhancement of cathodoluminescent and photoluminescent properties of Eu:Y2O3 luminescent films by vacuum cooling

D. Kumar, J. Sankar, K. G. Cho, V. Craciun, and R. K. Singh

Appl. Phys. Lett. 77, 2518 (2000); http://dx.doi.org/10.1063/1.1318938 (3 pages) | Cited 23 times

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This letter investigates the role of postdeposition oxygen treatments upon their luminescent properties by synthesizing Eu:Y2O3 films by pulsed laser deposition under different conditions and subjecting them to various postdeposition oxygen treatments. Our results have shown that Eu:Y2O3 films grown in 300 mTorr oxygen ambient and cooled in vacuum (10−6 Torr) after the termination of growth exhibit better photoluminescent and cathodoluminescent brightness than those grown in (i) vacuum and cooled in vacuum and (ii) 300 mTorr oxygen and cooled in 2 Torr oxygen. Two possible mechanisms have been proposed to explain these results. © 2000 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Tv Optical and dielectric properties related to treatment conditions
81.15.Fg Pulsed laser ablation deposition
85.45.Fd Field emission displays (FEDs)

Characterization of excimer-laser-annealed polycrystalline silicon films grown by ultrahigh-vacuum chemical vapor deposition

Ying-Chia Chen, YewChung Sermon Wu, I-Chung Tung, Chi-Wei Chao, Ming-Shiann Feng, and Huang-Chung Chen

Appl. Phys. Lett. 77, 2521 (2000); http://dx.doi.org/10.1063/1.1318937 (3 pages) | Cited 5 times

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Polycrystalline silicon (poly-Si) films grown by ultrahigh-vacuum chemical vapor deposition (UHVCVD) system and then annealed by excimer laser at room temperature have been investigated for the applications in polycrystalline silicon thin-film transistors (poly-Si TFTs). The results showed that the grain size of the laser-annealed poly-Si film decreased with laser energy density when a lower laser energy density below 157.7 mJ/cm2 was used. At about the threshold laser energy density ( ∼ 134.5 mJ/cm2), the finest grain structure could be obtained due to the partial melting in the top layer of the film. When the energy density of the excimer laser was larger than the threshold energy density, the large grain growth was initiated. The largest grain structure could be obtained at ∼ 184 mJ/cm2, while its surface roughness was better than that of the nonannealed UHVCVD poly-Si films. The surface roughening was suggested to arise from the specific melt-regrowth process but not the rapid release of hydrogen or capillary wave mechanism derived from laser-annealed amorphous silicon. By use of the laser-annealed UHVCVD poly-Si films as the active layer, the fabricated poly-Si TFT exhibited a field-effect mobility of 138 cm2/V s, a subthreshold swing of 0.8 V/dec, a threshold voltage of 3.5 V, and an on/off current ratio of ∼ 106. © 2000 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.82.Fk Semiconductors
78.66.Db Elemental semiconductors and insulators
78.40.Fy Semiconductors
85.30.Tv Field effect devices

Complete removal of threading dislocations from mismatched layers by patterned heteroepitaxial processing

X. G. Zhang, A. Rodriguez, X. Wang, P. Li, F. C. Jain, and J. E. Ayers

Appl. Phys. Lett. 77, 2524 (2000); http://dx.doi.org/10.1063/1.1319178 (3 pages) | Cited 9 times

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We report the effectiveness of patterned heteroepitaxial processing (PHP) in removing threading dislocations (TDs) from ZnSe epitaxial layers grown on GaAs substrates by metalorganic vapor phase epitaxy. The PHP approach used here involves postgrowth patterning of continuous epitaxial layers followed by annealing. In this study, each as-grown ZnSe/GaAs sample was first cut into pieces forming four types of samples, namely: (1) as grown, (2) postgrowth annealed, (3) postgrowth patterned, and (4) PHP prepared (patterned and annealed). The epitaxial layers with thicknesses of 2000–6000 Å were patterned to create 500–6000-Å-high and 3–70-μm-wide square mesas that were separated by 20 μm trenches. TD densities were determined by the etch pit density (EPD) technique and comparisons were made between the four types of samples. The first three types of samples exhibited EPDs of approximately 107 cm−2, which indicate that neither patterning alone nor annealing alone was effective at reducing TDs. In contrast, PHP resulted in a complete removal of TDs from 70 μm×70 μm square layers with thicknesses of >3000 Å. This corresponds to an EPD less than 2.0×104 cm−2, and at least a 500-fold reduction compared to as-grown layers; in fact, this value is even lower than that of the GaAs substrate (EPD=105 cm−2). Thus TDs can be removed in PHP by glide to the sidewalls, as promoted by the presence of image forces. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Dz II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Phase diagram of epitaxial ferromagnets: Erbium (0001) on sapphire (11math0)

C. S. Durfee and C. P. Flynn

Appl. Phys. Lett. 77, 2527 (2000); http://dx.doi.org/10.1063/1.1319182 (3 pages)

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We have accurately determined the elastic state and the magnetic phase diagram of epitaxially clamped Er on Al2O3 through the range of strong bulk magnetostriction. The elastic free energy is too small to explain the observed change of the Curie point. The additional required energy of ∼5% of the self-energy for full perpendicular magnetization must arise from differences of domain configuration between the magnetized bulk and the film. © 2000 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.55.-a Thin film structure and morphology

Y-junction carbon nanotubes

B. C. Satishkumar, P. John Thomas, A. Govindaraj, and C. N. R. Rao

Appl. Phys. Lett. 77, 2530 (2000); http://dx.doi.org/10.1063/1.1319185 (3 pages) | Cited 155 times

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Carbon nanotubes with junctions are considered to be of potential value in nanoelectronics. A simple pyrolysis procedure for producing Y-junction carbon nanotubes is described. The method involves the pyrolysis of the organometallic precursor, nickelocene, along with thiophene at 1273 K. Tunneling conductance measurements showed that at the Y junction, the I-V characteristics are asymmetric with respect to zero bias as in a junction diode. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
85.65.+h Molecular electronic devices
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.61.Wp Fullerenes and related materials
73.40.Gk Tunneling

Dislocation energetics in epitaxial strained islands

B. J. Spencer and J. Tersoff

Appl. Phys. Lett. 77, 2533 (2000); http://dx.doi.org/10.1063/1.1319186 (3 pages) | Cited 20 times

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We calculate (to first order in the Burgers vector) the energy of introducing dislocations into Stranski-Krastanow islands having equilibrium shape. These results suggest that misfit dislocations of different Burgers vector tend to segregate spatially within the islands, which may be a source of mosaic structure in films formed by island coalescence. © 2000 American Institute of Physics.
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61.72.Lk Linear defects: dislocations, disclinations
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
64.75.-g Phase equilibria
61.72.Bb Theories and models of crystal defects
66.30.Lw Diffusion of other defects

Pressure dependence of the blue luminescence in Mg-doped GaN

S. Ves, U. D. Venkateswaran, I. Loa, K. Syassen, F. Shahedipour, and B. W. Wessels

Appl. Phys. Lett. 77, 2536 (2000); http://dx.doi.org/10.1063/1.1319180 (3 pages) | Cited 1 time

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We report the hydrostatic pressure dependence of the blue luminescence band observed at ∼2.8 eV in heavily magnesium-doped GaN (GaN:Mg) epilayers grown on sapphire by metalorganic chemical vapor deposition. Photoluminescence (PL) studies carried out up to 6 and 8 GPa, respectively, at room and low (10 K) temperature show that the pressure-induced energy shift of this PL band is ∼26 meV/GPa. This blueshift is about 40% less than the shift observed for the band edge in GaN. A substantially smaller pressure coefficient suggests that the 2.8 eV PL transition is associated with the recombination via deep centers. © 2000 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
62.50.-p High-pressure effects in solids and liquids
71.55.Gs II-VI semiconductors

Photoirradiation effect on polymer light-emitting device: Separation between recombination zone and photo-oxidized defects

Kazuya Tada and Mitsuyoshi Onoda

Appl. Phys. Lett. 77, 2539 (2000); http://dx.doi.org/10.1063/1.1314888 (3 pages) | Cited 6 times

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The photoirradiation effect on the characteristics of a polymer light-emitting diode with a semitransparent metal cathode is studied. The electroluminescence intensity as well as the photoluminescence quantum efficiency decreases due to photoirradiation in air, while the external quantum efficiency of electroluminescence does not change. This suggests that not the formation of quenching defects but the degraded carrier transport/injection nature of the polymer mainly affects the emission property of the device and that the recombination zone is separated from the photo-oxidized defects. Two models of the separation, the layer model and the scattering model, are proposed. The validity of the two models depends on the penetration depth of oxygen in the polymer. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
61.82.Pv Polymers, organic compounds
61.41.+e Polymers, elastomers, and plastics
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Optical properties of high-quality CuInSe2 single crystals

A. V. Mudriy, I. V. Bodnar, I. A. Viktorov, V. F. Gremenok, M. V. Yakushev, R. D. Tomlinson, A. E. Hill, and R. D. Pilkington

Appl. Phys. Lett. 77, 2542 (2000); http://dx.doi.org/10.1063/1.1308525 (3 pages) | Cited 12 times

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CuInSe2 single crystals have been studied employing photoluminescence (PL), optical reflection (OR), optical absorption (OA) and wavelength derivative reflection (WDR) techniques at temperatures from 4.2 to 300 K. Exciton-related peaks were observed in the near-band-edge region of the PL spectra: several narrow lines, with full width at half maximum (FWHM) of about 0.3 meV, and two wider peaks (FWHM about 0.7 meV) at 1.0414 (A) and 1.0449 eV (B). The A and B peaks were also observed in the OR and OA spectra and identified as A and B free excitonic states. The narrow lines were attributed to bound exciton recombination on intrinsic defects. A third exciton resonance (C) was observed in the WDR spectra at 1.2779 eV. The crystal-field and spin-orbit splittings were derived to be 5.3 and 234.7 meV, respectively. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.40.Fy Semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.70.Ch Crystal and ligand fields
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